I'm coming back from about 20 plus years away from building and flying RC aircraft. During the hiatus I was able to hang on to one of my planes powered by an OS 40. The prop still turns with a little "gummy" feeling but there's still compression. I've pulled the head screws and was able to remove the head/cylendar sleeve and it all looks pretty good other than the carbon deposits on the top of the piston. The throttle is stuck so I think I need to soak it in something to get that free enough to disassemble. What's the best cours of action to get this enging back on line?